1. Field of the Invention
This invention relates to an electronic component of the type which comprises a resin package for enclosing inside parts, and at least one lead terminal projecting out from the package and bent at its root point. The present invention also relates to a method of bending the lead terminal. The present invention further relates to a method of mounting such an electronic component.
2. Description of the Prior Art
It is known to enclose various electronic elements, such as semiconductor chips, in a resin package for protection. In such an electronic component, each lead terminal is led out of the package and suitably bent for mounting onto a circuit board by soldering.
FIGS. 10 and 11 of the accompanying drawings show a typical prior art resin-packaged electronic component. Specifically, the component comprises a protective resin package 1' and a pair of lead terminals 2' projecting out of the package 1'.
Each of the lead terminals 2' is bent downward at the root point which is a position immediately adjacent to the package 1', as indicated by arrows A' in FIG. 12. The lead terminal is further bent at an intermediate portion inwardly toward the package (as indicated by solid lines in FIG. 10) or outwardly away from the package (as indicated by phantom lines in FIG. 10) to provide a bonding end which is used for mounting the electronic component to e.g. a circuit board by soldering.
The prior art electronic component of FIGS. 10-12 is advantageous in that the overall length L' of the component can be rendered relatively small because each of the lead terminals 2' is bent downward at the root point by utilizing a relatively sharp edge portion of the resin package 1'. Indeed, the lateral projecting amount S' of the lead terminal corresponds substantially to the thickness of the lead terminal itself in case the bonding end of the lead terminal is bent inwardly toward the package thereunder.
However, the utilization of the relatively sharp edge of the resin package 1' as a bending support results in concentration of bending stress at the root point of each lead terminal 2'. Thus, the lead terminal is liable to crack formation and may have a reduced strength at the bending root point. Further, since a bending force is directly applied to the package, it may be damaged, by chipping for example, at the sharp edge portion.
In view of the above problems, Japanese Patent Application Laid-open No. 1-230218 discloses a resin-packaged capacitor wherein each of lead terminals is conveniently bent by using a backup wire.
More specifically, as shown in FIGS. 13 and 14 of the accompanying drawings, the capacitor disclosed in the above-mentioned Japanese patent document comprises a protective resin package 1" and a pair of lead terminals 2". Each of the lead terminals 2" is bent downwardly about a cylindrical backup wire 3" which is arranged at an armpit-like portion of the capacitor, as indicated by arrows A" in FIG. 13. The backup wire 3" is removed after completing the bending operation, as clearly shown in FIG. 14.
Apparently, the backup wire 3" supports a round support for conveniently bending the lead terminal 2" without undue stress concentration at the bending point of the lead terminal and without direct application of a bending force to the resin package 1". However, the prior art of FIGS. 13 and 14 still has the following problems.
First, the backup wire 3" need be made of a relatively hard material to prevent compressive deformation of the wire at the time of performing the bending operation since otherwise it will be difficult or impossible to remove the backup wire after the bending operation. Thus, each of the lead terminals 2" will laterally project at least by an amount S" which is equal to the sum of the diameter D" of the backup wire 3" and the thickness T" of the lead terminal 2", consequently increasing the overall length L" of the capacitor.
Secondly, the need for removing the backup wire 3" increases the time required for making the capacitor, hence an increase of the production cost.
In the third place, when mounting the capacitor to a printed circuit board by soldering, there is a tendency that, due to insufficiency of used solder paste, the solder fillets which are formed at the connection between the lead terminals and the circuit board will not have a sufficient height as required for reliably bonding the capacitor. Thus, the bonding strength for the capacitor may become low. Indeed, this problem is also encountered in mounting any electronic component to a printed circuit board.